Impact of intentional avoidance of internal mammary nodes by VMAT in left chest wall irradiation
NARENDRA KUMAR BHALLA,
India
PO-1217
Abstract
Impact of intentional avoidance of internal mammary nodes by VMAT in left chest wall irradiation
Authors: NARENDRA KUMAR BHALLA1, Abhishek Puri2, Mohandass P2, Palanivelu D2, Manoharan M2, Pratibha Bhalla3
1Fortis Hospital , Department of Radiation Oncology, Mohali, India; 2Fortis Hospital , Department of Radiation Oncology, Mohali , India; 3University of Chicago , The College of Liberal Arts and Science , Chicago , USA
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Purpose or Objective
Adjuvant regional nodal irradiation (RNI) inclusive
of internal mammary nodal chain (IMC), remains contentious for locally advanced
carcinoma breast. This retrospective study proposes to assess planning outcomes
for IMC in left chest wall by Volumetric Arc Therapy (VMAT) with “intentional
avoidance”. Adjuvant regional nodal irradiation (RNI) inclusive
of internal mammary nodal chain (IMC), remains contentious for locally advanced
carcinoma breast. This retrospective study proposes to assess planning outcomes
for IMC in left chest wall by Volumetric Arc Therapy (VMAT) with “intentional
avoidance”.
Material and Methods
Ten patients with left sided locally advanced
carcinoma breast (post chemotherapy and Modified Radical Mastectomy) were
included. Monaco™ Treatment Planning System (TPS) was utilized to develop two
sets of plans (twenty) with uniform planning specifications. All subjects had
left sided Supraclavicular Fossa (SCF), Level III, IMC and Chest Wall
segmentation peer reviewed for uniformity by two separate physicians. Plan
evaluation using standard dose volume histogram (DVH) parameters had: 95% of
prescribed doses to CTV, Conformity Index (CI), Homogeneity Index (HI),
Integral dose (ID), Dmean, Dmax and dose volume received by critical structures
such as heart, left lung, right lung, liver, spinal cord and contralateral
breast. A 60% isodose coverage was clinically significant for “incidental” dose
to IMC after generation of VMAT with IMC (W-IMC) [as reference] & without IMC (WO-IMC) plans.
Results
An average of 8.6 nodes were involved in
histopathological assessment. Results were analyzed and recorded as W-IMC and
WO-IMC respectively: Dose prescription for 95% CTV was 97.6±1.5%, vs.
98.2±1.6%; Dmean Heart 783.6±106.5cGy vs. 774.1±108.0cGy, V20 Left Lung
29.1±0.5% vs. 28.8±1.5% CI 1.11±0.1 vs. 1.10±0.01; HI 0.975±0.01 vs.
0.977±0.02. No significant dose difference were seen in liver, spinal cord,
contralateral breast, and ID between W-IMC and WO-IMC plans (p>0.05). A
considerable variation in average incidental dose to 60% of IMC was recognized;
W-IMC (5176.8±63.4 cGy) vs. WO-IMC, (4257.1±38.6 cGy) (p<0.05).
Conclusion
Our initial exploratory abstract reveals that
inclusion of IMC for modulated radiation therapy has no substantial impact on
heart dose, even though it comes with a heightened risk of under dosage on
exclusion.